1. Field of the Invention
This invention relates generally to a predictive energy management system for a hybrid electric vehicle and, more particularly, to a predictive energy management system for a hybrid electric vehicle, where the system uses smart vehicle information, such as present location, time, 3-D maps, driving history, etc, to determine current and future engine and motor power commands.
2. Discussion of the Related Art
Hybrid electric vehicles use an engine and one or more electric motors to propel the vehicle to achieve better fuel economy and lower emissions than conventional vehicles. The engine output power does not have to equate power demands as in conventional vehicles. Generally the engine is used at high load demands and the motor is used at low load demands. The electric motor can supplement the power from the engine when the engine cannot sufficiently or efficiently provide the current power demands. The motor can also absorb the engine power and store it in a battery for later use. The engine can also be used to recharge the battery during prolonged use of the motor.
The battery state of charge (SOC) is an important consideration when determining if the motor should be used because a battery is more efficient if the battery state of charge is between an upper bound battery charge and a lower bound battery charge. The hybrid system also needs to be self-sustaining. Therefore, it is desirable to try and maintain the battery state of charge at or near a nominal value. Because it is desirable to have as small of a battery as feasible because of weight and cost requirements, it is necessary to be more selective with the charging and discharging of the battery to maintain the nominal battery state of charge as the motor is operated.
Known power control strategies for hybrid vehicles that determine the engine power and motor power are typically based on current driving conditions. Particularly, the hybrid vehicle controller will determine the combination of engine power and motor power depending on the current vehicle speed and torque requests from the vehicle operator in combination with other parameters, such as the battery state of charge. These power control inputs typically will be provided by look-up tables that have been generated for particular torque requests based on vehicle speed, battery state of charge, etc.
It is desirable to be able to predict future vehicle operating conditions and environment to make better use of the engine power and the motor power to further achieve better fuel economy and lower emissions. For example, if the vehicle controller knows that the vehicle will be traveling down a hill in the near future, it will know that the motor will be able to operate as a generator to charge the battery through regenerative braking when the vehicle goes down the hill. Therefore, it may be desirable to use more motor power than otherwise might be used as the vehicle approaches the hill so that the battery state of charge is first reduced to be later charged by the regenerative braking. Other future conditions, such as traffic information or highway travel, can also better prepare the vehicle controller for these driving conditions if they are known in advance.